Dextran was evaluated as a binder material for graphite electrode, silicon electrode, and Si/graphite composite electrode in Li-ion cells. The performance was also compared with poly(vinylidene fluoride) (PVDF) binder or lithium salt of poly(acrylic acid) (LiPAA) binder. A graphite-rich Si/graphite composite electrode shows a reversible capacity of about 525 mAh gr(-1) at a C/5 rate and has an excellent cycling stability. An interface study using impedance spectroscopy, X-ray photoelectron spectroscopy, and postmortem scanning electron microscopy analysis shows that the superior performance is due to the formation of a solid-electrolyte interface (SEI) layer that completely covers the surfaces of silicon and graphite. This could be attributed to a strong interaction between dextran through the shortly branched one-dimensional structure and silicon surface as evidenced by attenuated total reflection-infrared spectroscopy. This along with its low cost and environmentally friendly nature makes it an attractive binder material for Si/graphite composite electrodes in Li-ion batteries.